Methods and apparatus for coupling gas turbine engine components

ABSTRACT

A method facilitates assembling a gas turbine engine assembly including at least a first member and a second member. The method comprises inserting a threaded fastener through an opening formed in a flange, and providing at least one shank nut including a flanged mating end, an opposite non-mating end, and a body extending therebetween. The body includes an internal surface, an external surface, and a centerline extending between the body ends. The flanged mating end includes a substantially planar exterior surface that is aligned perpendicularly to the centerline and an annular groove that extends from the exterior surface at least partially towards the non-mating end. The method also comprises securing the assembly together such that the mating end is positioned flush against the flange and such that the threaded fastener extends at least partially into a bore extending through the shank nut and defined by the shank nut internal surface.

BACKGROUND OF THE INVENTION

This invention relates generally to coupling assemblies, and, moreparticularly, to methods and apparatus for coupling gas turbine enginecomponents together.

At least some known mechanical coupling assemblies used to couple gasturbine components together include a threaded fastener and a threadedconnector. More specifically, within at least some known applications,the threaded fastener is inserted through an opening formed in a flangeprior to a connector being threadably coupled to it for securing acomponent to the flange. At least some known flange openings arecounter-bored to enable a portion of the threaded fastener to remainrecessed with respect to an external surface of the flange after thefastener is coupled to the flange.

As the connector is threadably tightened to the fastener, clampingloading is induced to the flange. However, when counter-bored openingsare used, at least a portion of the clamp loading induced to the flangeis carried by the thinner portions of the flange that define thecounter-bore. Over time, the uneven load pattern stresses induced withinthe flange may cause the edges of the fastener opening within the flangeto roll inward and away from the threaded connector, in a conditionknown as “bolthole rolling.” Bolthole rolling may cause additionalstresses to be induced to the flange which over time may cause apremature failure of the flange.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for assembling a gas turbine engine assemblyincluding at least a first member and a second member is provided. Themethod comprises inserting at least one threaded fastener through afastener opening formed in a flange extending from the first member, andproviding at least one shank nut including a flanged mating end, anopposite non-mating end, and a body extending therebetween, wherein thebody includes an internal surface, an external surface, and a centerlineextending between the first and second ends, and wherein the flangedmating end includes a substantially planar exterior surface that isaligned perpendicularly to the centerline and an annular groove thatextends from the exterior surface at least partially towards thenon-mating end. The method also comprises securing the assembly togethersuch that the flanged mating end is positioned flush against the flangeand such that the threaded fastener extends at least partially into abore extending through the shank nut and defined by the shank nutinternal surface.

In another aspect, a shank nut for mating with a threaded matingcomponent is provided. The nut includes a flanged mating end, anopposite non-mating end, and a body extending therebetween. The flangedmating end includes an exterior surface that is substantially planar.The body includes an internal surface, an external surface, and acenterline extending between the first and second ends. The internalsurface defines a bore extending between the first and second ends. Thebore is sized to receive at least a portion of the mating componenttherein. The mating end exterior surface is perpendicular to the bodycenterline and includes a groove extending at least partiallycircumferentially around the body bore. The groove extends axially fromthe mating end exterior surface at least partially towards the nutnon-mating end.

In a further aspect, a coupling assembly for a gas turbine engine isprovided. The coupling assembly includes a flange including at least onefastener opening extending therethrough, and a shank nut for mating withthe threaded fastener. The at least one fastener opening is sized toreceive at least a portion of a threaded fastener therethrough. Theshank nut includes a flanged mating end, an opposite non-mating end, anda body extending therebetween. The flanged mating end includes asubstantially planar exterior surface. The body includes an internalsurface and an external surface. The body also includes a centerlineextending between the first and second ends. The internal surfacedefines a bore extending between the first and second ends. The bore issubstantially concentrically aligned with respect to the body and issized to receive at least a portion of the threaded fastener therein.The mating end exterior surface is perpendicular to the body centerlineand includes an annular groove extending generally axially from themating end exterior surface and at least partially towards the shank nutnon-mating end. The flange is coupled against the shank nut mating end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a cross sectional view of a portion of an exemplary embodiment ofa coupling assembly; and

FIG. 2 is an enlarged perspective view of the threaded connector usedwith the coupling assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a cross sectional view of a portion of an exemplary embodiment ofa coupling assembly 10 including a threaded connector or shank nut 12.FIG. 2 is a perspective view of threaded connector 12 that is used withcoupling assembly 10. Specifically, coupling assembly 10 includes atleast one flange 20, shank nut 12, and a threaded fastener (not shown).In one embodiment, the threaded fastener is a threaded bolt that isthreadably coupled to shank nut 12, as described in more detail below.Coupling assembly 10 is used to securely couple components together,such as gas turbine engine components. In the exemplary embodiment,coupling assembly 10 is used to couple adjacent mating portions of arotor shaft 14 together. In one embodiment, rotor shaft 14 is amulti-piece rotor shaft that is used with a CF6-80 gas turbine enginecommercially available from General Electric Aircraft Engines,Cincinnati, Ohio.

In the exemplary embodiment, each shaft portion 14 includes a couplingflange 20 that extends radially outward from an external surface 21 ofshaft 14 to enable adjacent portions of shaft 14 to be coupled together.It should be noted that in FIG. 1, although only one shaft portion 14 isillustrated, each shaft portion 14 includes a coupling flange or otherknown coupling means, that enables shaft portions 14 to be coupledtogether. Flange 20 includes a mating surface 22, an opposite couplingsurface 24, and at least one fastener opening 26 extending therebetween.In the exemplary embodiment, fastener opening 26 is extends through acounter-bored portion 28 of flange 20, such that a sidewall 30 definingcounter-bored portion 28 and opening 26 is obliquely oriented withrespect to surfaces 22 and 24. Accordingly, a thickness T of flange 20measured between coupling surface 24 and a sidewall 30 is variableacross counter-bored portion 28.

Shank nut 12 includes a flanged mating end 40, an opposite non-matingend 42, and a generally cylindrical body 44 extending therebetween. Inthe exemplary embodiment, body 44 has a substantially circularcross-sectional profile. In alternative embodiments, body 44 has othercross-sectional shapes. Body 44 has an external surface 50, an internalsurface 52, and a centerline 53 that extends between ends 40 and 42.Internal surface 52 defines a bore 54 that extends between body ends 40and 42. In the exemplary embodiment, bore 54 is concentrically alignedwith respect to body 44 and has a diameter D_(B) that is substantiallyconstant through bore 54. Internal surface 52 is threaded and includes aplurality of threads 60 that extend between body ends 40 and 42.Diameter D_(B) is sized to receive at least a portion of the threadedfastener therein.

In the exemplary embodiment, shank nut external surface 50 is taperedfrom flanged mating end 40 at least partially towards non-mating end 42,such that a wall thickness T_(W) of body 40 measured between bodysurfaces 50 and 52 is at least partially variably between body ends 40and 42. More specifically, in the exemplary embodiment, external surface50 is tapered from a hook 70 extending from body 40 at least partiallytowards non-mating end 42.

In the exemplary embodiment, hook 70 extends radially outward from body44 such that an outer end 71 of hook 70 is positioned a distance D₁forward of an end surface 72 of mating end 40. Distance D₁ enables hook70 to extend radially outward of an outer edge 74 of flange 20 such thathook 70 provides an anti-rotation feature to shank nut 12, as describedin more detail below. In the exemplary embodiment, hook 70 includes ascallop 76 which enables shank nut 12 to be easily visuallydistinguishable from other threaded connectors. In alternativeembodiments, shank nut 12 does not include hook 70.

A chamfer 80 is formed along mating end 40 at the edge 82 formed betweenbody external surface 50 and end surface 72. In the exemplaryembodiment, chamfer 80 is positioned diametrically opposite hook 70 andis formed substantially parallel to the width W_(H) of hook 70 ratherthan following the circular arc of edge 82. Because of installationspace limitations, in the exemplary embodiment, chamfer 80 enables shanknut 12 to be formed with a larger flange radius R_(F) at mating end 40.In alternative embodiments, shank nut 12 does not include chamfer 80.

In the exemplary embodiment, shank nut 12 also includes a shank barrel90 extending outward from mating end 40. Specifically, in the exemplaryembodiment, shank barrel 90 is substantially cylindrical and extends adistance D₂ from end surface 72 to a outer edge 92. Distance D₂ enablesshank barrel 90 to be swaged or outwardly flared such that shank nut 12is retained in an axial direction against flange 20 during assembly byshank barrel 90, as is described in more detail below. Shank barrel 90has a diameter D₄ defined by an outer surface 96 of shank barrel 90 thatis smaller than an inner diameter D₅ of flange fastener opening 26adjacent flange coupling surface 24.

A groove 100 is defined within mating end 40 and extends a distance D₆axially inward from end surface 72. In the exemplary embodiment, groove100 is annular and extends circumferentially around shank barrel 90 andbore 54. In an alternative embodiment, groove 100 extends only partiallycircumferentially around barrel 90. In another alternative embodiment,mating end 40 includes a plurality of grooves defined therein. As isdescribed in more detail below, groove 100 facilitates redistributingclamping loading radially outward from shank nut centerline 54 whenshank nut 12 is securely coupled in position.

During assembly of rotor shaft 14, initially shank nut 12 is positionedadjacent flange 20. Specifically, initially shank nut 12 is positionedsuch that shank nut mating end 40 is against flange coupling surface 24.Accordingly, shank barrel 90 extends at least partially through flangefastener opening 26. Shank barrel 90 is then swaged or flared using aknown flaring tool such that shank barrel 90 is forced outwardly againstflange fastener opening sidewall 30. Accordingly, once swaged, shankbarrel 90 facilitates retaining shank nut 12 in an axial direction inposition relative to, and against, flange 20.

A component to be coupled to rotor shaft 14 is then positioned adjacentshaft 14 such that a flange extending from that component is against themating surface 22 of flange 20. A threaded fastener is then insertedthrough the first component flange and through flange 20. Morespecifically, as the fastener is extended through flange 20, thefastener is rotated to be threadably coupled to shank nut 12. Becausehook 70 extends radially outward from an outer edge 74 of flange 20,hook 70 facilitates preventing nut 20 from rotating as the threadedfastener is torqued within nut 12.

Continued rotation of the fastener enables shank nut 12 to induce aclamping force to flange 20 such that the components of rotor shaft 14are securely coupled together. More specifically, shank nut groove 100facilitates redistributing clamping loading radially outward from shanknut centerline 54 such that the reaction loading is not induced throughcounter-bored portion 28, but rather is instead induced through aportion 100 of flange 20 that has a thickness T₁ that is thicker thanthat any thickness T measured within counter-bored portion 28. Moreover,the additional material thickness T₁ of flange portion 100 facilitatesstructurally enhancing the stiffness of flange 20 such that bolt rollingwithin flange fastener opening 26 is facilitated to be reduced as aresult of groove 100. Furthermore, the tapering of shank nut externalsurface 50 facilitates enabling the clamp load to more easily passbetween the nut threads 60 and mating surface 72.

After the threaded fastener has been securely coupled within shank nut12, shank nut non-mating end 42 is crimped against the threadedfastener. Crimping end 42 facilitates preventing shank nut 12 fromunthreading from the threaded fastener, such that end 42 provides aself-locking feature to nut 12.

The above-described coupling system is a cost-effective and reliablemeans for coupling components together. The shank nut includes anannular groove which displaces the mating surface of the nut radiallyoutward, such that clamp loading is redistributed radially outward fromthe nut bore. Accordingly, the clamp loading is carried by a thickerportion of the mating flange such that stresses induced to the flange,and/or bolt rolling of the fastener opening within the flange, arefacilitated to be reduced. As a result, the shank nut facilitatessecurely coupling components together in a cost-effective and reliablemanner

Exemplary embodiments of coupling assemblies are described above indetail. The assemblies are not limited to the specific embodimentsdescribed herein, but rather, components of each assembly may beutilized independently and separately from other components describedherein. For example, each shank nut component can also be used incombination with other coupling assemblies.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for assembling a gas turbine engine assembly including atleast a first member and a second member, said method comprising:inserting at least one threaded fastener through a fastener openingformed in a flange extending from the first member; providing at leastone shank nut including a flanged mating end, an opposite non-matingend, and a body extending therebetween, wherein the body includes aninternal surface, an external surface, and a centerline extendingbetween the first and second ends, and wherein the flanged mating endincludes a substantially planar exterior surface that is alignedperpendicularly to the centerline and an annular groove that extendsfrom the exterior surface at least partially towards the non-mating end;and securing the assembly together such that the flanged mating end ispositioned flush against the flange and such that the threaded fastenerextends at least partially into a bore extending through the shank nutand defined by the shank nut internal surface.
 2. A method in accordancewith claim 1 wherein securing the assembly together further comprisessecuring the assembly together such that the shank nut annular groovefacilitates reducing an amount of reaction loading induced to theflange.
 3. A method in accordance with claim 1 wherein securing theassembly together further comprises positioning the shank nut againstthe flange prior to inserting the threaded fastener through the assemblysuch that a shank barrel extending from the shank nut mating end extendsat least partially through the flange fastener opening.
 4. A method inaccordance with claim 3 wherein positioning the shank nut against theflange prior to inserting the threaded fastener through the assemblyfurther comprises outwardly flaring an end of the shank barrel such thatthe shank barrel axially retains the shank nut to the flange.
 5. Amethod in accordance with claim 1 wherein securing the assembly togetherfurther comprises securing the shank nut in position relative to theassembly such that a hook extending from the shank nut external surfacesubstantially prevents rotation of the shank nut relative to the flange.6. A method in accordance with claim 1 securing the assembly togetherfurther comprises crimping the shank nut non-mating end to provide aself-locking mechanism. 7-20. (canceled)